Center for Auditory Regeneration and Deafness
Human Auditory Neurophysiology Laboratory
The long term goal of the research in this laboratory is to understand the human brain mechanisms that underlie hearing, speech and language. The immediate and near-term goals are to learn the locations, boundaries, functional organizations and interconnections of those areas of human cerebral cortex engaged in processing speech information. This includes information derived from acoustic and visual cues, in silent background and in backgrounds filled with competing sound. The research involves direct electrophysiological recording from, and stimulation of, human cerebral cortex using arrays of electrodes implanted on the pial surface and within the brain parenchma of patients undergoing diagnostic studies and surgical treatment of medically intractable epilepsy. The work is carried out by a multidisciplinary team of researchers using a variety of complementary experimental and analytical methods.
The research is centered in the Human Brain Research Program (HBRP) at the University of Iowa, The HBRP is directed by Dr. Matthew Howard and is administratively housed within the Department of Neurosurgery. Programmatically, it is a part of the NIH-supported University of Iowa General Clinical Research Center (GCRC) as well as the Institute for Human Neurological Diseases.
The research team is drawn from the University of Iowa, the University of Wisconsin, Albert Einstein College of Medicine and Oxford University. This team represents the fields of neurosurgery, neurology, neuroanatomy, neurophysiology, psychology, audiology, electrical and computer engineering, mathematics and statistics.
Research Highlights
- Developed state-of-the-art methodology for recording from and electrically stimulating the cerebral cortex of subject-patients undergoing diagnosis and treatment of intractable epilepsy.
- Identified several auditory fields on the dorsal surface of the superior temporal gyrus, including field AI on the mesial aspect of Heschl’s gyrus. It was shown that different auditory fields are represented there based on their electrophysiological responses to simple and complex sound, including speech.
- Using the same stimulus paradigms, the response of primary auditory cortex in humans and monkeys to speech sounds was shown to be essentially the same. This finding bridges the gap in interpreting data obtained from this area in human and monkey.
- Identified an auditory field on the posterolateral aspect of the superior temporal gyrus and characterized many of its acoustic (including speech) response properties.
- Mapped the functional connections between physiologically identified fields on the supratemporal plane and posterolateral superior temporal gyrus using an electrical stimulation tract tracing technique. This finding is consistent with a hierarchical processing model proposed on the basis of anatomical and electrophysiological studies in non-human primates.
- Identified functional connectivity between posterolateral superior temporal gyrus and cortex more anterior to it. These provide the experimental evidence for a ventral processing stream postulated to be involved in auditory object recognition.
- Identified a functional connection between posterolateral superior temporal gyrus and the inferior frontal gyrus. This provides the first experimental evidence to support a model of speech and language first postulated by Wernicke more than a century ago.
- Identified an area on posterolateral superior temporal gyrus involved in the integration of auditory and visual speech information.
- Identified cortical sites which upon electrical stimulation led to suppression of sound perception and, in one case, suppression of tinnitus.
